The invention relates generally to patient support systems using inflatable cushions or mattresses to reduce patient interface pressures and, more particularly, to air loss mattresses which may be used on standard hospital beds.
In recent years, low air loss beds have come into extensive use and are commonly used in hospitals to prevent and treat the symptoms of immobility. Low air loss beds have been marketed by several companies like Mediscus Products Limited, Kinetic Concepts, Inc., Air Plus, Inc., and SSI Medical, Inc. Many of the products currently in use cost in excess of $10,000.00. However, the most common method of marketing today is to rent these beds to patients in hospitals which may be reimbursed by insurance, Medicare, or Medicaid. Typical rental fees range roughly from $50.00 to $200.00 or more per day. Few hospitals are willing or able to make the large capital expenditures necessary to maintain sufficient low air loss beds to supply patients.
There have been many other devices which have been utilized to attempt to prevent or treat the symptoms of immobility. A common symptom of immobility is decubitis ulcers, which are commonly referred to as bed sores. A primary cause of bed sores is the inability of a patient to move. When a patient is immobile for extended periods, pressure points can cut off the localized blood flow (such as in the skin adjacent a bony protuberance) when the localized pressure exceeds the capillary pressure. When the blood flow in the capillaries is blocked due to the pressure, the cells in that area begin to die and may result in the sore or wound which is called a bed sore. Mobile persons do not have this problem because they periodically move even when asleep, which minimizes the duration of capillary closure in any given area.
Many types of devices have been used to increase the comfort of an immobile patient. These have taken the form of feathers or other types of stuffing material In more recent years, foam has been used as well as innerspring mattresses. While these devices are useful for individuals who are not immobile, they do not provide adequate care for immobile patients. Many devices have been utilized with limited degrees of success to prevent or treat bed sores. Egg-crate type foam has been commonly used although its therapeutic value is questionable. Similar alternating pressure pads have been used. Both have the advantage of being very inexpensive. Waterbeds have also been used, but a waterbed suffers from the hammocking effect where the patient assumes a similar orientation to that of an individual in a hammock suspended between two points. Other types of devices which have been proposed have been non-fluidized sand beds. While the egg-crate foam has been commonly used, waterbeds and other types of similar devices have not met with much commercial success, nor are they considered to be of much therapeutic value.
In the early 1960's, studies were conducted in England by a Professor John T. Scales on the treatment of burn patients who had received skin grafts. When a burn patient receives a skin graft, shear applied to the graft may result in dislocation of the skin graft or layer of skin which has been grafted onto the burned area. This will often result in failure of the graft. Professor Scales originally proposed completely supporting a patient on a high volume of air similar to the principle of a hovercraft. This type of device became known as the levitation bed and is shown in U.S. Pat. No. 3,354,476 issued to John P. Scales. The levitation bed was further perfected in England as shown in U.S. Pat. Nos. 3,340,550 and 3,340,551 issued to Leslie A. Hopkins. Professor Scales and Mr. Hopkins worked together on these devices in the middle 1960's when Professor Scales was at Mt. Vernon Hospital and Mr. Hopkins was at Hovercraft Development, Ltd. Mr. Hopkins was a hovercraft skirt expert and utilized his expertise in this area to make the first workable high air loss bed which has been reported in medical journals. While the high air loss bed would support a patient on a very high volume of air and prevent any shear or damage to the skin, it proved to be impractical. It required a very high volume of air that had to be heated and humidified and was very costly to operate. While sound in theory, the high air loss bed was commercially doomed. Although tests were performed with the high air loss bed, it was eventually abandoned around 1970. In 1968, Mr. Hopkins invented what is now called the low air loss bed. This device is shown in British Patent No. 932,779. This device was further perfected by Professor Scales as shown in U.S. Pat. No. 3,822,425 which called for the use of water vapor permeable but water proof fabric.
At about the same time that Professor Scales and Mr. Hopkins were working on the high air loss bed and low air loss bed, Mr. Thomas S. Hargest came up with the air fluidized bed, or "Bead bed." An example of this is shown in U.S. Pat. No. 3,428,973. Although a geologist by training, Mr. Hargest began work as a clinical engineer in Galveston, Texas at a burn hospital. There, with the assistance of several physicians, Mr. Hargest adapted general air fluidized bed technology (typically used for sandblasting reservoirs) to make a bed which would support a patient. The air fluidized bed (or "bead bed," as it became known) had the advantage of little or no shear, which was very useful for burn patients.
Although both the low air loss bed and the air fluidized bed grew out of research in burns, it soon became apparent that they were also useful for just treating patients that suffered from immobility. The low air loss bed and the air fluidized bed share the common feature of distributing the support of a patient over a much larger surface area of the patient. Such pressure distribution reduced any pressure points that would otherwise exceed capillary closure pressure and reduce blood flow to the point of damage to the skin. Unfortunately, although both the low air loss bed and the air fluidized bed were invented in the late 1960's, neither enjoyed much commercial success for over ten years.
In the 1970's, several other devices were devised which were of some use in treating and preventing the symptoms of immobility. Those devices included the oscillating bed which was invented by Dr. Frances X. Keane which is shown in U.S. Pat. No. 3,434,165. Another such device was the net bed such as shown in U.S. Pat. No. 4,357,722. Other devices included the Stryker brand frame and the Circle Electric bed. Various alternating pressure pads such as those marketed by Gaymar also came into use. While each of those devices have some therapeutic value, apparently they have yet to achieve the commercial success of low air loss beds and air fluidized beds in treating and preventing immobility.
There have been many improvements made in the low air loss bed which was invented by Mr. Hopkins and Professor Scales. Much of this work was done at Air Cushion Equipment, Ltd. which was owned and operated by Mr. Leslie A. Hopkins. Mr. Roy Henvest, Mr. Robert Cook, and Mr. Graham Westerling-Norris. Improvements in the low air loss bed were also made by Mr. Frank Ducker and Mr. William B. Hunt at Mediscus Products, Ltd., who made the first commercial low air loss bed in about 1973.
For many years, there have been attempts at making an inexpensive device that would serve the purpose of the low air loss bed. Air fluidized beds which typically weigh as much as one ton could not be considered in the same category as low air loss beds, particularly the portable type. The attempts to make such an inexpensive device began with Mr. Hopkins as early as 1968 and were continued by Mr. Hopkins at Air Cushion Equipment Limited for almost ten years. They were carried on by Mr. Robert Cook at Air Cushion Equipment Limited and then later by Mediscus Products, Ltd., but all such attempts have met only limited success. In lieu of no commercially practical low air loss support mattress, until now the market has resorted largely to other less costly but questionably effective devices such as the alternating pressure pads and egg-crate foam mattresses as a substitute for relieving patient interface pressures.
From the beginning, it was Mr. Hopkins'dream to build a poor man's low air loss bed. This is exemplified in his initial low air loss device shown in his original patent which was little more than a mattress. However, the direction of development did not go that way and beds after Mr. Hopkins'initial bed were generally full-sized beds with complete frames. Mr. Hopkins again proposed a form of portable low air loss bed in about 1976, when he was a consultant to Mediscus Products Limited which is shown in British Patent No. 1,545,806. Design work continued at Air Cushion Equipment, Limited in the middle 1960's on the portable low air loss bed and most of the design was made by Mr. Robert Cook. Air Cushion Equipment, Limited was retained by Mediscus Products, Limited and the work there of Mr. Cook resulted in the first commercial low air loss mattress which was intended to be usable on any type of bed frame. The device which was conceived and initially constructed by Mr. Cook at Air Cushion Equipment, Limited is exemplified in U.S. Pat. No. 4,525,885. Another attempt at a less expensive low air loss bed is shown in British Patent No. 2,134,379B. None of these devices have enjoyed any commercial success, in particular the device shown in U.S. Pat. No. 4,525,885 was commercially abandoned because of hygiene problems.
A more recent attempt at an inexpensive support mattress is shown in U.S. Pat. No. 4,803,744 which is assigned to Hill-Rom Company, which is probably the largest hospital bed manufacturer in the U.S. As of yet, this device has not achieved any significant commercial success nor is it believed that it is likely to.
There are believed to be many thousands of patients who suffer the complications of immobility but who receive no treatment on air fluidized beds or low air loss beds because of the substantial costs involved and the lack of funds. This is particularly acute in nursing homes where the products are badly needed but generally unavailable because of the cost. While many other devices such as the egg-crate foam and other systems have been used, they have not solved the problem, nor will they ever.
It is an object of the present invention to provide a relatively low-cost and simple air mattress which would serve the purpose of a low air loss mattress and could be used on standard hospital beds while being commercially practical as well as therapeutically effective. It is another object of the invention to provide a lightweight, inexpensive mattress which is therapeutically similar to low air loss bed and the air fluidized bed but which does not cost as much to manufacture or maintain.
In his initial patent on the low air loss bed, Professor Scales proposed the use of waterproof but water vapor permeable material. This type of material has gained widespread use with the advent of Gortex brand laminate which has established itself in the medical area as being a highly effective and useful material. While air permeable (or high air loss) Gortex material (i.e., one of the nylon materials laminated with the Goretex brand laminate and manufactured by the W. L. Gore Co.) has been available, the most commonly used version of Gortex in low air loss beds is air-impermeable but water vapor permeable. This Gortex material or laminate is typically attached to a woven nylon material. For comfort and therapeutic reasons, it is often desirable or necessary to provide air flow around the patient. It is generally accepted that skin which remains in contact with liquid or excessive vapor is more subject to skin breakdown. This is readily recognized by anyone who spends a large amount of time in water which causes a wrinkling of the skin. Both the air impermeable and air permeable Gortex materials largely eliminate such problems. There have been other types of water vapor permeable materials which have also been proposed, but they have not obtained the widespread acceptance and use as has Gortex brand material. Since the initial commercialization of the low air loss bed, one of its largest benefits has been considered its ability to control the environment with low air loss around the patient as well as control the pressure through the low loss of air. A patient would not find a typical air mattress to be comfortable for any extended period of time because it is typically made of material which is completely airtight and water vapor impermeable and which does not have careful pressure regulation. Furthermore, a patient would sweat and be less comfortable when in contact with a vinyl material which was generally impermeable. Others have proposed use of air and water impermeable materials with holes punched therein to provide an air exhaust for their low air loss beds.
It is an object of the present invention to combine the benefits of low air loss beds and the use of water vapor permeable materials in a low cost mattress. It is also an object of the invention to provide the benefits of low air loss beds and low air loss therapy in an inexpensive mattress.
While the present invention requires an air supply blower, it is the object of the present invention to be able to utilize a relatively small and inexpensive blower. Air flow around a patient, however, may also cause some cooling of the patient's skin more particularly in the extremities of a patient. Studies have also indicated that slightly elevated temperatures may enhance the healing process in certain applications. Therefore and for other reasons, another object of the invention is to provide thermal controls for comfort and therapy of a patient supported on a mattress.
It is a further object of the invention to provide for adjustable pressure differentials in various sections of the mattress to provide comfort to compensate for weight distributions which vary from patient to patient or from time to time as a given patient's position may change. Typically, for any given patient there is more weight in the buttocks area than on the heels and the head so pressure differentials are desirable in order to properly support the patient lying on the mattress, particularly if the patient's upper body is elevated toward a sitting position.
Still another object of the present invention is to provide a relatively level patient support surface with adaptations to help prevent the patient from rolling or sliding to either side of the patient support surface.
It is another object of the present invention to provide a low cost, inexpensive low air loss support system which combines the therapeutic benefits of use of a water vapor permeable material and airflow around the patient as well as separate sections which have adjustable pressures. The intent is to achieve all of these objects with an affordable mattress that can be used on regular hospital beds or other support surfaces and which is inexpensive to manufacture and use and which may even be disposable.
Many other objects of the invention will be apparent from the following summary and detailed disclosures, particularly when viewed in light of the claims and drawings appended hereto.